If SWTOR is like other MMOs then somewhere down the line there's going to be additional classes added. I've said it before than if this happens I think it'll be something like the Noble class that we've seen in the SW tabletop games for several years now. Leia, Padme and Bail are some of the iconic characters which you can't really recreate in this game which also makes me feel that something like the Noble class will happen down the line.
Of course, I doubt a Noble would actually be a senator as running around the galaxy would get in the way of a full time political career. Yeah, all three of the others I mentioned we'ren't afraid to get their hands dirty, but those moments were the exception rather than the rule.
This brings up, however, the main issue with such a class "What would their story be?" On that I can only speculate. But behind the scenes powerplays would make great storytelling and allow for morally grey choices not unlike some of the Fallout games. Add in a few days of that guy with the eyepatch who hangs around Padme and it might be workable.